1. Field of the Invention
The present invention relates generally to underground pipe for use in sewers, storm drains, pen stocks, culverts and the like, and more specifically to a composite pipe structure including a metal core interposed between a pair of polymer layers providing structural support to the pipe.
2. Description of the Related Art
Metal pipe has been widely used for draining, culverts and other similar fluid conduits. Although susceptible to abrasion, there are several advantages associated with metal pipe over conventional concrete pipe, due to its comparatively high strength and low weight. These characteristics render metal pipe relatively inexpensive to manufacture, ship and handle while permitting its use in applications which require it to support substantial soil overburden. Moreover, metal pipe may achieve enhanced structural characteristics by forming the pipe to include corrugations or ribs.
One deficiency of metal pipe is that it is susceptible to corrosion and excessive abrasion, and therefore, use of metal pipe may be restricted primarily to culvert and storm drain applications. In storm drain applications, such metal pipe is particularly susceptible to extensive abrasion caused by the movement of gravel, dirt, sand, etc. therethrough. Such excessive abrasion frequently degrades metal pipe to a point where leakage of the contents of the pipe therefrom becomes a major concern. Additionally, such abrasion may, in some instances, be sufficient to adversely affect the structural integrity of the pipe, and consequently result in structural failure of the pipe wherein the overburden crushes a portion of the pipe, thereby effectively plugging the pipe and substantially reducing or eliminating flow therethrough.
In addition to the foregoing, conventional metal pipe used in buried storm drain applications frequently encounters substantial problems associated with its operational environment. More specifically, the pipe experiences abrasion during the process of back-filling the gravel and dirt on top of the buried pipe, wherein the metal may be scratched or damaged during the back-filling process. Furthermore, long term exposure of the exterior of the metal pipe within the burial environment may serve to corrode the exterior of the pipe while water and debris flowing through the interior of the metal pipe degrades the pipe through abrasion.
Accordingly, there is a need in the art for an improved pipe structure, which protects the metal used in forming the pipe, while at the same time, reducing the overall cost of the pipe.